Existing apparatuses for purification of polluted water, for example, include purification apparatuses and operation methods in which for the purpose of filtering separation of pollutant particles of a few μm or more in particle size or separating them according to specific gravity differences, a coagulant capable of supplying aluminum ion or iron ion is added to the polluted water as pretreatment for separation treatment, so that the pollutant particles are collected in the flocs whose matrixes are aluminum hydroxide and iron hydroxide, to form large and dense pollutant particle clumps of a few hundreds to a few thousands μm in particle size such that polluted water is purified through separation based on filtration or specific gravity difference.
Also, included are purification apparatuses and operation methods in which a magnetic powder is added contemporarily with a coagulant to form the magnetic flocs, and the magnetic flocs are trapped and separated by exerting magnetic force, so that polluted waster is purified. In this type of purification apparatuses and operation methods, the metal ion in the added coagulant is collected in the separated flocs or magnetic flocs in the form of hydroxide, and the flocs are dehydrated with a centrifugal separator or a belt press machine and then subjected to incineration disposal, discard disposal, or composting disposal.
Accordingly, conventional purification apparatuses and operation methods require continuous addition of coagulants as expendables in every operation.
However, the coagulants are expensive, thereby causing increase in operation cost, and furthermore, the operators have to convey and resupply the coagulant at regular intervals which poses a problem that the operation cost is increased by the personnel cost to be increased accordingly.
Thus, in order to improve the efficiency in such a purification apparatus and an operation method, as disclosed in JP-A-8-24515, the separated matter obtained by coagulation and separation is first added with a strongly acidic aqueous solution such as sulfuric acid, so that flocs or magnetic flocs are made to be situated in a strongly acidic solution falling in the non-coagulation condition range, and the flocs are thereby disintegrated. Addition of a strongly acidic aqueous solution such as sulfuric acid to this solution elutes the ions of such metals as aluminum from the metal hydroxides, forming an aqueous solution of aluminum sulfate. The solution itself thus obtained is a coagulant, and can be reused as a coagulant.
Further, under this condition, the pollutant particles and magnetic powder are eliminated from the flocs, and the magnetic powder can be magnetically separated by applying the magnetic force of a magnet, recovered, and reused.
Furthermore, the concentration of the pollutant particles can further be increased by sedimentation, filtering separation with a membrane and the like, and furthermore, by removal based on separation.
On the other hand, when the magnetic field is made extremely high by use of a superconductor magnet based on a super conductor bulk magnet or a coil type superconductor magnet as a magnet used for magnetic separation, if the iron based coagulant is used instead of a magnetic powder to form flocs on the basis of iron hydroxide, namely, the flocs are formed with weakly magnetic iron hydroxide, the flocs can be magnetically separated without the use of the magnetic powder. In this case, accordingly a magnetic powder is not used, and hence no facilities for supplying a magnetic powder and recovering the magnetic powder from the sludge are needed.
In the above described treatment method, in order to regenerate coagulants an acid agent or an alkali agent is needed to be continuously added as expendable, and hence there has occurred a problem that the operation cost is increased by the cost defrayed for these two types of reagents and by the personnel cost defrayed for the labor of the periodic supply of these two types of reagents.
Further, in the case where the pollutant is crude oil, there occurs a problem that the floc disintegration by acid or alkali treatment alone allows the pollutant to remain mixed in the sludge so that the pollutant cannot be separated the from the sludge, and the regenerated coagulant is made to be mixed with the crude oil so that the coagulant cannot work as a satisfactory coagulant.
Furthermore, in the case where a purification apparatus is used on the sea-based platform for an offshore oil field, there occurs a problem that the periodic supply of the coagulant requires the transportation by a helicopter or a devoted ship, which is accompanied by a high transportation cost and a high unloading cost, thus resulting in an increase of the purification operation cost.
Moreover, in the case where are removed the pollutant matters such as the oil in the ballast water (For establishing the balance of a ship after unloading, sea water is filled in the vacant space in the ship, and the sea water is discharged into the sea immediately before loading.) in a crude oil tanker, a natural gas carrying vessel, an ore carrying vessel, or the like, and the bacteria, plankton and the like in the loaded sea water, periodic resupply of coagulants requires the purchase of chemicals at the anchoring sites, and is accompanied with a problem that the chemicals to be used are not easily obtainable depending on the anchoring sites. Further, there occurs a problem that harmful plankton in the separated or removed/recovered sludge cannot be disinfected as the sludge remain separated so that the sludge is needed to be disinfected. Further, in the case where a volume reduction apparatus is needed to be installed for the recovered sludge, the installation space has to be secured, with an accompanying problem of acquiring the space aboard.